A secondary battery, which is easily applied to various product groups and has electrical characteristics such as high energy density, is universally applied not only for a portable device but also for an electric vehicle (EV) or a hybrid electric vehicles (HEV), an energy storage system or the like, which is driven by an electric driving source. The secondary battery is attracting attention as a new environment-friendly energy source for improving energy efficiency since it gives a primary advantage of reducing the use of fossil fuels and also does not generate by-products by the use of energy at all.
A battery pack applied to the electric vehicle or the like has a structure in which a plurality of cell assemblies, each including a plurality of unit cells, are connected in series to obtain a high output. In addition, the unit cell may be repeatedly charged and discharged by means of electrochemical reactions among components, which include a positive electrode current collector, a negative electrode current collector, a separator, an active material, an electrolyte and the like.
Meanwhile, as the need for a large capacity structure is increasing along with the utilization as an energy storage source in recent years, there is a growing demand for a battery pack in which a plurality of battery modules, each including a plurality of secondary batteries connected in series and/or in parallel, are integrated.
Since the battery pack is manufactured so that a plurality of secondary batteries are compactly aggregated in a narrow space, it is important to easily release the heat generated by each secondary battery. Since the charging/discharging process of the secondary battery is performed by electrochemical reactions as described above, the battery may be affected by ambient temperature conditions. For example, if the charging/discharging process is performed under severe temperature conditions such as an extremely low temperature or an extremely high temperature at which the optimum temperature is not maintained, the charging/discharging efficiency of the battery is lowered, and thus it may be difficult to ensure the performance for normal operation.
In addition, due to thermal conduction resistance existing between members used for configuring a cooling structure, the cooling efficiency intended at the designing stage may not be obtained in many cases.
Thus, there is a high need for a battery module that gives a high-output large-capacity power, ensures easy designing, and is excellent in life characteristics, safety and cooling efficiency.